Transport of 1,5-anhydro-D-glucitol into insulinoma cells by a glucose-sensitive transport system

The uptake of 1,5-anhydro-D-glucitol (1,5-AG) occurs by passive mechanisms in cells or tissues that have passive glucose transporters. It is known that serum 1,5-AG concentrations are reduced in patients with diabetes mellitus. To elucidate the metabolism of this substance and its physiological role in pancreatic β-cells, we assayed 1,5-AG transport in the insulinoma-derived cell lines, RINr and MIN6. Both cell lines showed an insulin-insensitive, concentration-dependent uptake of 1,5-AG with a saturation time of approximately 120 min, and most of the 1,5-AG in the cytoplasm was in the free form. A biphasic saturation curve was obtained using a wide range of 1,5-AG concentrations, suggesting that accumulation was mediated by a high affinity and a low affinity transporter. The high affinity transporter had a K_m of 10.4 in RINr cells and 13.0 mM in MIN6 cells, and the low affinity transporter had a K_m of 131 in RINr cells and 211 mM in MIN6 cells. Uptake of 1,5-AG was markedly inhibited by phloretin and cytochalasin B, but was only slightly affected by phloridzin. Uptake of 1,5-AG was markedly inhibited by glucose at physiological concentrations (1.0–10 mM), as well as by galactose and mannose. The 1,5-AG concentration required to inhibit 2-deoxyglucose uptake exceeded that of glucose by >100 times, being much higher than the physiological concentrations of 1,5-AG. These results indicate that the 1,5-AG carrier system in insulinoma cells is distinct from that in either the somatic cells or renal tubular cells. These findings also suggest that a unique 1,5-AG transport system is present in pancreatic β-cells.